Graphite Negative Electrode Coating for Longer Battery Cycle Life
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium secondary batteries using natural graphite negative electrode active materials face issues with volume expansion/shrinkage and side reactions with the electrolyte solution during charging/discharging, leading to poor durability and cycle life.
Innovation Solution
A negative electrode for lithium secondary batteries is developed using spheroidized natural graphite particles with inserted pitch in their pores, forming a carbon layer to reduce specific surface area and pore volume, thereby minimizing side reactions and volume changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If natural graphite is used as negative electrode active material, then capacity and adhesion strength are improved, but volume expansion/shrinkage during charging/discharging worsens durability
Solution Approach 1:
The patent uses spheroidized natural graphite particles as the core material and coats them with a carbon layer formed from pitch or polymer resin. This composite structure combines the high capacity and adhesion strength of natural graphite with the dimensional stability of the carbon coating, resolving the contradiction between capacity and durability by protecting the graphite from excessive expansion/shrinkage while maintaining its electrochemical performance.
Solution Approach 2:
The patent applies a thin carbon film coating on the surface of spheroidized natural graphite particles. This carbon layer acts as a flexible shell that accommodates the volume changes of the graphite during charging/discharging, preventing particle fracture and maintaining electrode integrity, thus improving durability without sacrificing capacity.
2Strength
If pitch or polymer resin is coated on natural graphite particles to form carbon layer, then adhesion is improved, but carbon layer is not formed in pores resulting in high specific surface area and side reactions with electrolyte
Solution Approach 1:
The patent utilizes the porous structure of spheroidized natural graphite particles and fills these pores with pitch material before forming the carbon layer. This ensures that the carbon coating penetrates into the pores of the graphite particles, reducing the exposed specific surface area and preventing side reactions with the electrolyte while maintaining the adhesion benefits of the carbon layer.
Solution Approach 2:
The patent performs preliminary filling of the pores with pitch material before the carbonization process. This preliminary action ensures that the pores are already occupied by pitch that will form the carbon layer, preventing electrolyte access to the high-surface-area graphite pores and eliminating side reactions before they can occur during battery operation.
3Ease of operation
If spheroidized natural graphite is used, then rolling property is improved, but volume expansion/shrinkage during charging/discharging still occurs
Solution Approach 1:
The patent coats spheroidized natural graphite particles with a carbon layer that acts as a flexible shell. This shell maintains the spherical shape and good rolling properties of the particles while accommodating the volume expansion and shrinkage that occurs during lithium insertion and extraction, preventing particle fracture and electrode degradation.
Solution Approach 2:
The patent changes the physical and chemical parameters of the graphite surface by coating it with carbon material. This modification alters the surface properties to reduce volume changes during electrochemical cycling while preserving the spherical morphology and rolling characteristics that facilitate good electrode formation and electrode-to-current collector contact.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively suppresses solid electrolyte interphase growth and volume expansion/shrinkage, enhancing the durability and cycle life of lithium secondary batteries while maintaining high energy density and capacity.
Implementation Method 1
pitch is present in the plurality of pores
Implementation Method 2
pressing the negative electrode mixture slurry on the at least one surface of the negative electrode current collector
Data Source
AI summary
A negative electrode for a lithium secondary battery including a negative electrode active material layer. The negative electrode active material layer is formed by steps of coating a negative electrode mixture slurry including spheroidized natural graphite particles as a negative electrode active material on at least one surface of a negative electrode current collector, followed by drying and pressing the negative electrode mixture slurry on the at least one surface of the negative electrode current collector. The spheroidized natural graphite particles include a plurality of pores. The negative electrode active material layer has a Brunauer-Emmett-Teller (BET) specific surface area of the negative electrode active material layer after the pressing is larger than a BET specific surface area of the negative electrode active material layer before pressing. A difference in the BET specific surface area before and after pressing ranges from 0.9 m2/g to 1.2 m2/g.